In the drilling of oil wells, gas wells, and the like, it is conventional practice to use a drilling fluid, such as a drilling mud to enhance the efficiency of the operation. When a drilling mud is used, it is continuously circulated from a storage area on the surface, downward through the drill pipe, and then upward through the borehole to the surface. The purpose of the mud is to remove drilled solids, such as cuttings and formation carvings, from the borehole to the surface. The fluid acts not only as a carrier, but also serves to cool and lubricate the drill bit, and to prevent pressure from being lost if a void or high-pressure gas pocket is encountered. Typically, drilling fluids for maritime drilling are more environmentally friendly than drilling fluids for land based use, but even so, most drilling fluids and muds contain a number of components, including barium, hematite, iron sulfite, and the like as weighting agents. Drilling muds and drilling fluids are typically mixed with oil to produce the final form of mud. In many areas of offshore drilling the oil component is known as synthetic oil. These synthetic oils exhibit minimal toxicity toward aquatic life and possess desirable Theological and filtration control properties for use in drilling fluids as compared to ordinary oil. The use of synthetic oils, particularly oleogomerized olefins, for drilling fluids has recently been patented these are referred to a synthetic oil based drilling muds or (SBM). For example, Mercer et al. in U.S. Pat. No. 5,096,883 discloses the use of compositions consisting essentially of branched paraffin having between 16 and 40 carbon atoms per molecule (such as the hydrogenated dimer of 1-decene) for this use. Also, Patel et al. in U.S. Pat. No. 5,189,012 discloses the use of compositions comprising branched chain oligomers.
Drilling muds are usually classified as either water-based muds or oil-based muds, depending upon the character of the continuous phase of the mud, although water-based muds may contain oil and oil-based muds may contain water. Water-based muds (WBM) conventionally comprise a hydratable clay, usually of the montmorillonite family, suspended in water with the aid of suitable surfactants, emulsifiers and other additives including salts, pH control agents and weighting agents such as barite. The water makes up the continuous phase of the mud and is usually present in an amount of at least 50 percent of the entire composition; oil may be present in minor amounts but will typically not exceed the amount of the water so that the mud will retain its character as a water-continuous phase material. Oil-based muds on the other hand, generally use a hydrocarbon oil as the main liquid component with other materials such as clays or colloidal asphalts added to provide the desired viscosity together with emulsifiers, gellants and other additives including weighting agents. Water may be present in greater or lesser amounts but will usually not be greater than 50 percent of the entire composition; if more than about 10 percent water is present, the mud is often referred to as an invert emulsion, i.e. a water-in-oil emulsion. In invert emulsion fluids, the amount of water is up to about 40 weight percent with the oil and the additives making up the remainder of the fluid.
Oil-based muds (OBM) were traditionally formulated with diesel oil or kerosene as the main oil component as these hydrocarbon fractions generally posses the requisite viscosity characteristics. They do, however, posses the disadvantage of being relatively toxic to marine life and the discharge of drilling muds containing these oils into marine waters is usually strictly controlled because of the serious effects which the oil components may have on marine organisms, particularly those which are commercially important for food. For this reason, offshore drilling rigs must return oil-based muds to shore after they have been used whereas water-based muds may generally be discharged into the ocean without any deleterious effects. The recycling of the OBM has become extensive and therefore in that respect an environmentally desirous outcome of the environmental movement. While the reuse of the OBM is environmentally friendly the use of diesel as the oil phase has a deleterious effect in that oil is left on the cuttings, which are discarded overboard.
OBM's may be made environmentally acceptable by the use of oils which posses low inherent toxicity to marine organisms and good biodegradability. These properties are associated in hydrocarbons with extremely low aromaticity. For these reasons, drilling fluids based on linear paraffins, olefins, alkanes and esters are considered desirable, and these are known as synthetic based muds (SBM). In recent years the environmental impact of overboard cuttings disposal both SBM and WBM has come under scrutiny by the regulatory environmental agencies.
One of the primary concerns is what is known as the mounding effect. This occurs when earthen cuttings, that are naturally and unavoidably generated during the drilling process, are deposited next to the drilling rig creating mounds or hills. These mounds are not simply objectionable they are environmentally damaging in themselves. As the organic components in the mounds begin to biodegrade they create a chemical oxygen demand (COD), which removes the locally available oxygen from the sea floor. This process consumes the available oxygen (less is available at lower depths); limits further biodegradation, limits sea life growth, and creates dead zones in deep ocean drilling locales. It is unknown how long it takes for surface oxygen to re-oxygenate the ocean floor but estimates from years to decades have been proposed. This problem has been investigated extensively in the North Sea drilling regions and approximately two million tons of cuttings have been located and are being considered for remediation due to this mounding effect.
Recent Environmental Protection Agency and Canadian National offshore Board Resource Board (CNORB) environmental impact studies have shown that the use of SBM's is superior to all other methods of drilling with the single environmental stressor of cuttings disposition. The EPA in its 2001 protocol went so far as to recommend the use of SBM's over WBM's due the recycling and reuse of SBM's. This protocol did lower the total acceptable amount of synthetic oil on cutting prior to overboard disposal but stated that the total environmental impact of using SBM's with overboard disposal was less than the total impact of transporting said cuttings to shore.
This invention addresses the further remediation of the cutting produced from use of SBM, WMB, and OBM. It will be utilized in conjunction with and after the solids control equipment that would already be on the drilling rig
An object of the present invention is to provide an additive, which can be added to drilling fluids that have been used in the drilling process to make the organic contaminates found in SMB's, WBM's and OBM's available to indigenous marine life as a food.
Another object of the present invention is to provide and environmentally safe method for remediating drilling muds so that “mounding” does not occur on the sea floor near drilling rigs, creating “dead zones” for marine life near the rigs.
A further object of the invention is to create an inexpensive method for remediating drilling muds and drilling fluids so that the drilling fluids do not need to be transferred from the rig to land for disposal, and can be safely disposed of at sea off the drilling rig.